It is well-known that the geometrical characteristics of the indents on prestressing wire used in the manufacture of prestressed concrete railroad ties affect the magnitude of the transfer length. In particular, it has been shown that such parameters as indent depth, indent volume and indent sidewall angle all affect transfer length, with indent volume being a major influence. Previous research has shown that the larger the indent volume, the shorter the transfer length. For full load bearing capacity, it is important that the transfer length not exceed the distance to the rail seat. Consequently, transfer length has been identified as a key diagnostic parameter for evaluating the load bearing capability of prestressed concrete railroad crossties. Furthermore, it has been proposed for use as a valuable quality control parameter. Ongoing research, as well as previously published research results, also indicates that the geometry of the prestressing wire indents plays a major role in the formation of cracking. This is particularly important in the manufacture of concrete ties intended for high speed rail applications. Cracking and debonding of prestressing wires associated with ties in service can result in severe splitting and complete tie failure. It is therefore not sufficient to guarantee a safe transfer length alone, without consideration of the cracking propensity. The wire specifications in standard ASTM A881 are intended to promote quality prestressed railroad tie behavior; however, the detailed causes of cracking and splitting, and the specific indent features that are responsible, are not well-known from a quantitative perspective. Until recently, inspection of prestressing wire indent properties consisted of sampling a few indents from a small segment of wire, providing very limited statistical information on wire indent properties. To address this deficiency, a high-resolution automated non-contact optical wire indent scanning system has been developed for completely and rapidly characterizing all relevant indent geometrical parameters. The system is capable of measuring large segments of wire to yield statistically significant samples of all relevant indent parameters including indent depth, indent width, indent sidewall angle, indent pitch, and indent volume. The current state-of-the-art in this system development, along with some new insights based on recent indent scanning results, will be presented. This system represents a valuable tool to aid in identifying the key indent geometrical features related to cracking. The overall goal is to quickly assess critical indent parameters, so as to ensure high-quality bond and eliminate in-track tie splitting failures.

Pre-stressed concrete railroad ties must meet requirements during service life. Using pre-stressed wires in concrete members enhances load-carrying capacity of concrete ties. It is important to ensure that pre-stressed forcing is introduced well before rail seat where the high impact load is applied. The required length of wire to fully transfer pretension forcing to concrete member is referred as transfer length. In order to shorten the transfer length, wires with improved indentation are used. As the transfer length is shortened, the high amount of stress concentration at the interface of wire-concrete can lead to longitudinal splitting cracks in concrete railroad ties. Splitting crack can occur either right after de-tensioning or during service life. It has been observed that concrete properties and components can highly affect crack formation and propagation. In this research, the effect of coarse aggregate on the splitting cracks of concrete railroad ties was investigated. To assess the impact of coarse aggregate features on splitting crack performance, fracture toughness test was done on three-point bend prisms. The specimens were made of four different coarse aggregate including crushed aggregate and well-rounded aggregate. It was observed that angularity and coarseness of aggregate increases the fracture toughness of concrete by 20%. Then, the same mixes were used in fabrication of pre-stressed prisms with different cover length to evaluate actual performance of splitting cracks after de-tensioning. The wires were tensioned up to 7000 Ib per wire and de-tensioned when concrete strength of 4500 psi is reached. The results of crack area/length of splitting cracks showed that increasing angularity can significantly improve splitting cracks resistance.

A ballast layer is used to facilitate drainage and load transferring in railroad track structure. With tonnage accumulation, fine materials, such as coal dust, clay, locomotive sand, degraded ballast aggregate, and other small particles, will penetrate into the clean and uniformly graded ballast layer causing contamination, usually referred as fouling. Fouling is unfavorable to railroad track performance due to the reduced drainage and consequent engineering challenges including but not limited to mud pumping, excessive settlement, and reduced bearing capacity. Previous research has investigated the mechanical behavior of the fouled ballast in both the laboratory and the field environment. However, the fundamental mechanism that governs the manner in which the fouling materials are transported and accumulated in the ballast layer is not thoroughly understood. Researchers at the University of South Carolina have initiated the effort to investigate the fouling process in the ballast layer. High-fidelity computational fluid dynamics (CFD) simulation is used to study the fluid flow patterns in order to quantify the transport behavior of the fine particles within the ballast layer and potential impact to the track performance and drainage. Specifically, the ballast layer is treated as a porous material, and the fouling materials are modeled as distinct individual particles to assess the probability of their trajectory location. This paper presents the preliminary results of the simulated path of the fouling materials in the ballast layer under seepage, and demonstrates the capability of the developed algorithm to quantify the effects of the ballast layer characteristics on fouling materials transport. The findings from this study will be beneficial for optimizing shoulder ballast cleaning or undercutting practices.

Railroad ballast as a layer of track substructure performs important tasks such as increasing the bearing capacity of the sleepers, providing large voids for drainage and resisting the forces applied to the super-structure. Contamination of ballast as the result of ballast breakdown known as breakdown fouling can prevent ballast from performing its job and also affects the engineering properties of ballast. This paper discusses the drained static triaxial testing on granite ballast material with different amount of breakdown fouling and water content. Large-scale triaxial equipment was used for this testing program at the University of Massachusetts, Amherst. These tests were performed to study the effect of fouling and water content, on the strength properties and degradation characteristics of railroad ballasted track. Ballast with three different fouling percentages from clean to highly fouled ballast (<5%, 15% and 30%) and four water contents from dry to field capacity were tested under three different confining pressures. The results show that although an increase in moisture degrades the fouled ballast, increase in breakdown fouling at constant moisture conditions increases the strength of the ballast.

The performance of ballasted railway systems is commonly compromised by the infiltration of fine material into the voids of the ballast. This sand and finer grained materials in the ballast is known as fouling. Increased fouling can cause decreases in hydraulic conductivity and shear strength of the ballast, as well as reduce stiffness and resilient modulus of the overall track system. These problems can cause gradual deterioration of the track, which could eventually require maintenance. One of the largest source of fouling comes from ballast breakdown resulting from abrasion caused under repeated loading. This study aims to investigate the effects of fouling from ballast breakdown on the bearing capacity of the substructure that supports the rail superstructure. Previous investigations at the University of Massachusetts Amherst utilized large scale 10-inch (25.4 cm) diameter triaxial tests on granitic ballast with fouling from ballast breakdown. The tests were run with fouling contents of 0% (clean ballast), 15%, and 30% and at water contents varying from dry ballast to field capacity. Confining pressures of 5 psi (34.5 kPa), 10 psi (68.9 kPa) and 15 psi (103.4 kPa) were used in this series of tests. Using the results from these tests, the Mohr-Coulomb strength properties can be determined for each case. This study will make use of the strength properties obtained from the results of these tests and apply them using two commonly used bearing capacity analyses. The first model is the Meyerhof and Hanna Method which considers the track as a continuous footing over a layered system. This model considers two modes of failure; punching of an individual sleeper, and track system bearing. The second model applied is the slope stability method, which uses a two-dimensional limit equilibrium approach and the method of slices to determine a factor of safety against slope stability. This analysis is commonly performed using various software programs. In this study, SLOPE/W from the GeoStudio software package is utilized for analysis. The factors of safety resulting from the bearing capacity analysis using these two methods will be compared for each of the test configurations performed, which will help to confirm the results of the analyses. Since the Mohr-Coulomb strength properties change with the degree of fouling and the water content of the ballast, it is expected that this will have some effect on the bearing capacity of the track substructure. The results of these analyses showing the effects of water content and fouling of ballast on overall track substructure bearing capacity are presented in this paper.

Recent North American railway trends signify a transition to increased axle loads and higher train speeds. The use of concrete crossties is common practice in these applications for a variety of reasons, including higher load-carrying capacity and improved ability to maintain proper track geometry. Currently, prestressed concrete monoblock crossties share many geometric and structural properties regardless of manufacturer. For multiple reasons, some manufacturers are investigating the potential benefits of new geometries for crosstie design. One alternative currently being explored is to modify the length and cross-section of the crosstie in order to increase the flexural capacity while using a similar amount of material. In this paper the benefits and implications of these changes will be explored both through theoretical calculations and laboratory testing. This alternative design will be evaluated and compared to concrete crossties representative of those currently found in North America. Comparison of the designs will be based on structural cracking at critical locations along the crosstie. These results were used to provide guidance on critical design parameters for concrete crossties capable of withstanding future loading and performance demands.

This paper describes the conduct of the first of a series of quasi-static compression tests of rail passenger equipment being done to examine occupant volume strength. Specifically, this program is investigating methods of evaluating occupant volume integrity when loads are placed along the collision load path of the occupant volume. Budd Pioneer car 244 has been chosen as the test article to examine alternative occupant volume loading strategies. Since this car has been involved in several impact tests as part of a previous research program, it is important to verify the structural integrity of the vehicle before conducting an alternative loading test. Although the vehicle has been modified with crash energy management crush zones at both ends, the occupant volume between the body bolsters is unmodified from the original structure. The 800,000-pound compressive strength test will be used to ensure the structural integrity of the car is intact. Before the conduct of this test, repairs were made to the crush zone. These repairs included replacement of trigger elements in the form of shear bolts and shear rivets. Additionally, energy absorbing elements were removed from the pushback coupler and primary energy absorbers because they would not contribute to the load path of this test. Steel blocks were added to the sliding sill element, enabling it to contact the fixed sill and enhancing the load-bearing capacity of the sliding-fixed sill connection. Preliminary results of this test include an overall description of the test procedures, discussion of permanent deformation observed during the test, and presentation of finite-element simulation results. Detailed analysis of test results, including strain gage data, is ongoing. The test results are being compared with the finite-element model results in support of the next tests planned for this series. The next two tests will evaluate the carbody when it is loaded along its collision load path to establish the elastic limit and crippling strength.